The homeotic protein AGAMOUS controls microsporogenesis by regulation of SPOROCYTELESS

The Arabidopsis homeotic gene AGAMOUS (AG) is necessary for the specification of reproductive organs ( stamens and carpels) during the early steps of flower development(1-3). AG encodes a transcription factor of the MADS-box family that is expressed in stamen and carpel primordia. At later stages of development, AG is expressed in distinct regions of the reproductive organs(2-5). This suggests that AG might function during the maturation of stamens and carpels, as well as in their early development. However, the developmental processes that AG might control during organogenesis and the genes that are regulated by this factor are largely unknown. Here we show that microsporogenesis, the process leading to pollen formation, is induced by AG through activation of the SPOROCYTELESS gene (SPL, also known as NOZZLE, NZZ), a regulator of sporogenesis(6,7). Furthermore, we demonstrate that SPL can induce microsporogenesis in the absence of AG function, suggesting that AG controls a specific process during organogenesis by activating another regulator that performs a subset of its functions.